Biochemical effects of sex hormones on human endometrium will be studied in whole tissue and separated glands and stroma obtained at various phasis of the menstrual cycle, as will as in cultures of these specimens and of cells derived from them. The following enzymatic activities will be used as indicators of the effect of estrogens and progestins: estradiol 17Beta dehydrogenase, peroxidase, ornithine decarboxylase, and alkaline phosphatase. The responsiveness to hormones will be correlated with the presence of estrogen and progesterone receptors. As part of this study, the variations of steroid receptor levels during the cell cycle in synchronized cultures and the day-to-day changes in these levels in non-synchronized cultures will also be investigated.